Fixed #33288 -- Made SQLite introspection use information schema for relations.

Previous solution was using brittle and complex parsing rules to
extract them from the SQL used to define the tables.

Removed a now unnecessary unit test that ensured the removed parsing
logic accounted for optional spacing.

2 files changed, 6 insertions, 70 deletions

diff --git a/django/db/backends/sqlite3/introspection.py b/django/db/backends/sqlite3/introspection.py
index bcf11e1751..7c5c159b64 100644
--- a/django/db/backends/sqlite3/introspection.py
+++ b/django/db/backends/sqlite3/introspection.py
@@ -1,4 +1,3 @@
-import re
 from collections import namedtuple
 
 import sqlparse
@@ -117,61 +116,16 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
 
     def get_relations(self, cursor, table_name):
         """
-        Return a dictionary of {field_name: (field_name_other_table, other_table)}
+        Return a dictionary of {column_name: (ref_column_name, ref_table_name)}
         representing all foreign keys in the given table.
         """
-        # Dictionary of relations to return
-        relations = {}
-
-        # Schema for this table
         cursor.execute(
-            "SELECT sql, type FROM sqlite_master "
-            "WHERE tbl_name = %s AND type IN ('table', 'view')",
-            [table_name]
+            'PRAGMA foreign_key_list(%s)' % self.connection.ops.quote_name(table_name)
         )
-        create_sql, table_type = cursor.fetchone()
-        if table_type == 'view':
-            # It might be a view, then no results will be returned
-            return relations
-        results = create_sql[create_sql.index('(') + 1:create_sql.rindex(')')]
-
-        # Walk through and look for references to other tables. SQLite doesn't
-        # really have enforced references, but since it echoes out the SQL used
-        # to create the table we can look for REFERENCES statements used there.
-        for field_desc in results.split(','):
-            field_desc = field_desc.strip()
-            if field_desc.startswith("UNIQUE"):
-                continue
-
-            m = re.search(r'references (\S*) ?\(["|]?(.*)["|]?\)', field_desc, re.I)
-            if not m:
-                continue
-            table, column = [s.strip('"') for s in m.groups()]
-
-            if field_desc.startswith("FOREIGN KEY"):
-                # Find name of the target FK field
-                m = re.match(r'FOREIGN KEY\s*\(([^\)]*)\).*', field_desc, re.I)
-                field_name = m[1].strip('"')
-            else:
-                field_name = field_desc.split()[0].strip('"')
-
-            cursor.execute("SELECT sql FROM sqlite_master WHERE tbl_name = %s", [table])
-            result = cursor.fetchall()[0]
-            other_table_results = result[0].strip()
-            li, ri = other_table_results.index('('), other_table_results.rindex(')')
-            other_table_results = other_table_results[li + 1:ri]
-
-            for other_desc in other_table_results.split(','):
-                other_desc = other_desc.strip()
-                if other_desc.startswith('UNIQUE'):
-                    continue
-
-                other_name = other_desc.split(' ', 1)[0].strip('"')
-                if other_name == column:
-                    relations[field_name] = (other_name, table)
-                    break
-
-        return relations
+        return {
+            column_name: (ref_column_name, ref_table_name)
+            for _, _, ref_table_name, column_name, ref_column_name, *_ in cursor.fetchall()
+        }
 
     def get_primary_key_column(self, cursor, table_name):
         """Return the column name of the primary key for the given table."""
diff --git a/tests/introspection/tests.py b/tests/introspection/tests.py
index b55714f93e..d138e71bd6 100644
--- a/tests/introspection/tests.py
+++ b/tests/introspection/tests.py
@@ -1,5 +1,3 @@
-from unittest import mock, skipUnless
-
 from django.db import DatabaseError, connection
 from django.db.models import Index
 from django.test import TransactionTestCase, skipUnlessDBFeature
@@ -152,22 +150,6 @@ class IntrospectionTests(TransactionTestCase):
             editor.add_field(Article, body)
         self.assertEqual(relations, expected_relations)
 
-    @skipUnless(connection.vendor == 'sqlite', "This is an sqlite-specific issue")
-    def test_get_relations_alt_format(self):
-        """
-        With SQLite, foreign keys can be added with different syntaxes and
-        formatting.
-        """
-        create_table_statements = [
-            "CREATE TABLE track(id, art_id INTEGER, FOREIGN KEY(art_id) REFERENCES {}(id));",
-            "CREATE TABLE track(id, art_id INTEGER, FOREIGN KEY (art_id) REFERENCES {}(id));"
-        ]
-        for statement in create_table_statements:
-            with connection.cursor() as cursor:
-                cursor.fetchone = mock.Mock(return_value=[statement.format(Article._meta.db_table), 'table'])
-                relations = connection.introspection.get_relations(cursor, 'mocked_table')
-            self.assertEqual(relations, {'art_id': ('id', Article._meta.db_table)})
-
     def test_get_primary_key_column(self):
         with connection.cursor() as cursor:
             primary_key_column = connection.introspection.get_primary_key_column(cursor, Article._meta.db_table)